Many communication systems utilize high performance cables normally having four pairs or more that typically consist of two twisted pairs transmitting data and two receiving data as well as the possibility of four or more pairs multiplexing in both directions. A twisted pair is a pair of conductors twisted about each other. A transmitting twisted pair and a receiving twisted pair often form a subgroup in a cable having four twisted pairs. High-speed data communications media in current usage include pairs of wire twisted together to form a balanced transmission line. Optical fiber cables may include such twisted pairs or replace them altogether with optical transmission media (fiber optics).
When twisted pairs are closely placed, such as in a communications cable, electrical energy may be transferred from one pair of a cable to another. Energy transferred between conductor pairs is undesirable and referred to as crosstalk. The Telecommunications Industry Association and Electronics Industry Association have defined standards for crosstalk, including TIA/EIA-568B for Category 5e and proposed ISO/EC 11801 Category 6. The International Electrotechnical Commission has also defined standards for data communication cable crosstalk, including ISO/EEC 11801. One high-performance standard for 100 MHz cable is ISO/IEC 11801, Category 5. Additionally, more stringent standards are being implemented for higher frequency cables including Category 6 and Category 7, which includes frequencies of 200 and 600 MHz, respectively. Transmission rates of as much as 10 G-base-T employing 10 Gigabit Ethernet over copper at frequencies of 650 MHz or higher are now either anticipated or included as new industry standards emerge. Industry standards cable specifications and known commercially available products are listed in Table 1.
TABLE 1INDUSTRY STANDARD CABLE SPECIFICATIONSANIXTERANIXTERTIA CAT 6XP6XP7ALL DATA ATDRAFT 10R3.00XPR3.00XP100 MHzTIA CAT 5eNov. 15, 2001November 2000November 2000MAX TEST100MHz250MHz250MHz350MHzFREQUENCYATTENTUATION22.0db19.8db21.7db19.7dbPOWER SUM32.3db42.3db34.3db44.3dbNEXTACR13.3db24.5dbPOWER SUM10.3db22.5db12.6db23.6dbACRPOWER SUM20.8db24.8db23.8db25.8dbELFEXTRETURN LOSS20.1db20.1db21.5db22.5db
In conventional cable, each twisted pair of conductors for a cable has a specified distance between twists along the longitudinal direction. That distance is referred to as the pair lay. When adjacent twisted pairs have the same pair lay and/or twist direction, they tend to lie within a cable more closely spaced than when they have different pair lays and/or twist direction. Such close spacing increases the amount of undesirable cross-talk that occurs. Therefore, in many conventional cables, each twisted pair within the cable has a unique pair lay in order to increase the spacing between pairs and thereby to reduce the cross-talk between twisted pairs of a cable. Twist direction may also be varied. Along with varying pair lays and twist directions, individual solid metal or woven metal air shields, i.e. aluminum laminated to polyethylene terephthalate (PET) shields and/or woven metal such as braid shields, can be used to electro-magnetically isolate pairs from each other or isolate the pairs from the cable jacket and the surrounding environment.
Shielded cable, although exhibiting better cross-talk isolation, is more difficult, time consuming and costly to manufacture, install, and terminate. Individually shielded pairs must generally be terminated using special tools, devices and techniques adapted for the job, also increasing cost and difficulty.
One popular cable type meeting the above specifications is Unshielded Twisted Pair (UTP) cable. Because it does not include shielded pairs, UTP is preferred by installers and others associated with wiring building premises, as it is easily installed and terminated. However, UTP fails to achieve superior cross-talk isolation such as required by the evolving higher frequency standards for data and other state of the art transmission cable systems, even when varying pair lays are used.
Some cables have used supports in connection with twisted pairs. These cables, however, suggest using a standard “X”, or “+” shaped support, hereinafter both referred to as the “X” support. Protrusions may extend from the standard “X” support. The protrusions of these prior inventions have exhibited substantially parallel sides.
The document, U.S. Pat. No. 3,819,443, to Sun Chemical Corporation, hereby incorporated by reference, describes a shielding member comprising laminated strips of metal and plastics material that are cut, bent, and assembled together to define radial branches on said member. It also describes a cable including a set of conductors arranged in pairs, said shielding member and an insulative outer sheath around the set of conductors. In this cable the shielding member with the radial branches compartmentalizes the interior of the cable. The various pairs of the cable are therefore separated from each other, but each is only partially shielded, which is not so effective as shielding around each pair and is not always satisfactory.
The solution to the problem of twisted pairs lying too closely together within a cable is embodied in three U.S. Pat. No. 6,150,612 to Prestolite, U.S. Pat. No. 5,952,615 to Filotex, and U.S. Pat. No. 5,969,295 to CommScope incorporated by reference herein, as well as an earlier similar design of a cable manufactured by Belden Wire & Cable Company as product number 1711A. The prongs or splines in the Belden cable provide superior crush resistance to the protrusions of the standard “X” support. The superior crush resistance better preserves the geometry of the pairs relatives to each other and of the pairs relative to the other parts of the cables such as the shield. In addition, the prongs or splines in this invention preferably have a pointed or slightly rounded apex top which easily accommodates an overall shield. These cables include four or more twisted pair media radially disposed about a “+”-shaped core. Each twisted pair nests between two fins of the “+”-shaped core, being separated from adjacent twisted pairs by the core. This helps reduce and stabilize crosstalk between the twisted pair media. U.S. Pat. No. 5,789,711 to Belden describes a “star” separator that accomplishes much of what has been described above and is also herein incorporated by reference.
However, these core types can add substantial cost to the cable, as well as excess material mass which forms a potential fire hazard, as explained below, while achieving a crosstalk reduction of typically 3 dB or more. This crosstalk value is based on a cable comprised of a fluorinated ethylene-propylene (FEP) conductors with low smoke PVC jackets as well as cables constructed of FEP, PVDF, and ECTFE jackets with FEP insulated conductors. for meeting NFPA 262 plenum applications for fire retardant and smoke suppression requirements. For riser applications (i.e. UL 1666, etc.), properly PVC jackets with polyolefin conductors are useful for meeting the U.S. standards, however, globally the need for halogen free jackets continues.
Cables where no separation between pairs exist will exhibit less desirable cross-talk values. When pairs are allowed to shift based on “free space” within the confines of the cable jacket, the fact that the pairs may “float” within a free space can reduce overall attenuation values due to the ability to use a larger conductor to maintain 100 ohm impedance. The movement occurs when the cable is put on new reels or on a reelex box during installation and stress on the conductor may cause electrical degradation. As the jacket proximity to the conductors is further removed, the electrical properties between conductors or conductor pairs may also improve. FIG. 8B is an example of the present invention which assists greatly in providing further separation of the cable jacket from individual or paired conductors. The trade-off with allowing the pairs to float is that the pair of conductors tend to separate slightly and randomly. This undesirable separation contributes to increased structural return loss (SRL) and more variation in impedance.
One method to overcome this undesirable trait is to twist the conductor pairs with a very tight lay. This method has been proven impractical because such tight lays are expensive and greatly limit the cable manufacturer's throughput and overall production yield. An improvement included by the present invention to structural return loss and improved attenuation is to provide a central circular ring region with various extending protrusions for pair separation.
The central ring portion can optionally include a hollow region to act as a hollow duct which is available for the future filling with optical fiber or coaxial cable or twisted pair conductors. Inside the central ring portion it is possible to have a second inner section that includes either a smooth or rifled surface as needed for blown finer applications. The fiber optic portions may be blown by gaseous means (normally air) or pulled into the hollow region with a pull tape. The fiber optics may be installed in the hollow duct in advance of the insertion of conductor pairs and an overall jacket. Also, future filling of the hollow ducts may occur with any of the communications media (fiber, coax, twisted pair, etc.). This ability to “future fill” gives the cable additional “dual” functionality and addresses the concern that installers share regarding the need to remove or add new wire and cable to existing plenum or non-plenum areas carrying older media.
Other improvements have been shown and filed in U.S. application US 2003/0037955/A1 filed at the United States Patent and Trademark Office on Aug. 25, 2001 and published Feb. 27, 2003 and subsequent PCT international publication number WO 03/021607 A1, filed May 1, 2002 and published 13 Mar. 2003.
Another improvement, and one that is included by the present invention, is to provide a circular ring region which is surrounded by rounded lobes in a symmetric diamond-like geometry that defines as many as four separate regions for pair separation and derivatives thereof. Again the central ring portion can optionally include a hollow region to act as an air blown fiber (ABF) duct which is available for filling with optical fiber or for the aforementioned coaxial or twisted pair applications.
A third improvement included by the present invention is to provide a hollow four-petal or “daisy” shaped arrangement with a central core that may or may not be hollow, and derivatives thereof—again to allow for pair separation. Individual or paired conductors are placed within the hollow petals as required depending on electrical, mechanical, and flammability design requirements. If the central region is hollow, the possibility again exists for that region to act as an air blown fiber (ABF) duct which is available for filling with optical fiber.
Still another improvement included by the present invention is to provide cross-like arrangement of varying geometric design and derivatives thereof. One such arrangement is a more conventional cross-like separator section with “rifled” sections extending outward into four quadrants away from the central region. This rifled cross is then encased within an outer insulated layer which is itself shaped in an identical cross except that the dimensions of this outer cross is larger than the rifled inner cross and functions as a “skin”. In this manner the separator uses less material than a conventional cross separator and thus reduces the BTU content within a jacketed (or even an unjacketed) cable. An optimal design that meets the stringent fire retardancy and smoke suppression requirements as well as the electrical needs, includes the use of an outer solid skin of either FEP or PVC sufficient to reduce flame and smoke over a foamed insulation material with a very low (nearer to 1.00 the better) dielectric constant. To pass recent CMP-50 requirements, lower fuel loads are very helpful. To reduce fuel loads, the addition of air and reduction of material are both useful methods for achieving the desired goals of improved flammability, smoke generation, and electrical properties of any cable construction using separators of the present invention. Dual extrusion is a commonly known method that can allow for a dual insulation design capable of providing such a product. Dual extrusion also allows for more sophisticated designs where lowering BTU content is important, as for example in the IEC C332-3B1 and B2 test protocols for European applications. Use of a pull tape within these constructions, the tape itself constructed from fire retardant, smoke reducing materials, is also part of the present invention and provides another avenue to meet the needs of upgrading existing cable installations when new internal communications media must be provided. Industry standards European Flammability Standards are listed in Table 2.
TABLE 2European Flammability SpecificationsClassTest MethodsClassification Criteria (1)Additional ClassificationAcEN ISO 1716PCS ≦2.0 MJ · kg −1 (2)—B1cEN 50266-2-x (3)FS ≦ 1.75 m; andSmoke production (5) andAndTHR600s ≦ 7.5 MJ; andFlaming droplets/particles (6);Peak RHR ≦ 15 kW; andAndFIGRA ≦ 120** W · s−1Acidity/Corrosivity (7)EN 50265-2-1H ≦ 425 mmB2cEN 50266-2-x (3)FS ≦ 2.00 m; andSmoke production (5) andAndTHR600s ≦ 15 MJ; andFlaming droplets/particles (6);Peak RHR ≦ 50 kW; andAndFIGRA ≦ 150** W · s−1Acidity/Corrosivity (7)EN 50265-2-1H ≦ 425 mmC1cEN 50266-2-y (4)FS ≦ 2.0 m; andSmoke production (5) and600sTHR600s ≦ 15 MJ; andFlaming droplets/particles (6);AndPeak RHR ≦ 50 kW; andAndFIGRA ≦ 150** W · s−1Acidity/Corrosivity (7)EN 50265-2-1H ≦ 425 mmC2cEN 50266-2-y (4)FS ≦ 2.5 m; andSmoke production (5) and600sTHR600s ≦ 35 MJ; andFlaming droplets/particles (6);AndPeak RHR ≦ 100 kW; andAndFIGRA ≦ 250** W · s−1Acidity/Corrosivity (7)EN 50265-2-1H ≦ 425 mmDcEN 50265-2-1H ≦ 425 mmFlaming droplets/particles (6); AndAcidity/Corrosivity (7)EcNo performance determined**provisional figures
Yet another improvement included by the present invention is to provide variations on the cross-like arrangement by adding “zig-zag” with and without “sickle-like” endings regions instead of “rifled” sections extending outward into four quadrants away from the central region.
For all these configurations, a major purpose of the inventive design of these separators is to provide contributions to improved attenuation, power sum NEXT (near end cross talk), power sum ACR (attenuation cross-talk ratio) and ELFEXT (equal level far end cross-talk) by providing for better control of spacing of the pairs, adding more air-space, and allowing for “pair-twinning” at different lengths. Additional benefits include reduction of the overall material mass required for conventional spacers, which greatly contributes to flame and smoke reduction. The other major purpose is to allow for “future” or concurrent filling of any media such as optical, twisted pair, or coax conductors with sufficient spacing so that electrical and optical integrity is maintained.
In recent years, electro-optical equipment has begun to replace electronic equipment for certain applications, such as telecommunication and data communication networks. This trend should continue because the electro-optical equipment has inherent advantages over purely electronic equipment. These advantages include a broader bandwidth for signal transmission, greater storage capability for data, and inherent immunity to electromagnetic interference. Given these advantages of electro-optical equipment, fiber optic cables have become increasingly important because they transmit information and signals between the various pieces of electro-optical equipment.
The appearance of these cables resembles electrical cables, but fiber optic cables are smaller in size and lighter in weight. Fiber optic cables comprise optical fibers and other cable elements which are protected from the external environment by an external jacketing. These cables may be of a traditional design with the fibers surrounded by strength members and protective elements in the cable core or of a more non-traditional, loosely-bundled type with the fibers contained loosely within tubes or ducts in a cable core.
According to U.S. Pat. No. 4,997,256, optical fiber units may be suitable for installation by the force of a fluid flowing through a passage. The unit, in this case, includes at least one optical fiber and at least one interstitial cord. The fibers and cords are of the same diameter. They are bundled and surrounded by a first sheath that is formed of a material having a high Young's modulus. An outer sheath, of foamed polyethelene may surround the first sheath. More particularly, the invention described includes an improvement in the blowing and transmission properties of such an optical fiber unit.
The objects of the invention can be achieved by an optical fiber unit of a type that is to be installed by the drag force of a pressure fluid flowing through a pipe, containing at least one optical fiber and more than one interstitial cord which are bundled and surrounded by an inner and outer sheathing to provide a unitary assembly, which inner sheath is made of a resin that has a high Young's modulus and that exhibits small residual strain during the application of sheathing. The outer sheath is made of a foamed polyethylene.
Another object of this invention can be attained in an effective way if the interstitial cord used in the optical fiber unit has substantially the same outside diameter as the optical fiber. Further, the object of this invention can be attained in a more effective way if at least one of the interstitial cords has a sufficient strength to work as a rip cord that assists in ripping away the inner and outer sheaths when the optical fiber is withdrawn from the optical fiber unit during end preparations.
In the case of the present invention, the central “hollow” portion of the support-separator can act as the duct for accommodating the inventive entity described. The duct could be composed of polybutylene terephthalate, amorphous nylon or other suitable materials such as described in the U.S. Pat. No. 4,997,256 patent. Essentially all other aspects of the '256 patent which include installing optical fiber into predisposed duct can be incorporated into the present invention using the central hollow portions of the support separator as the predisposed duct.
U.S. Pat. No. 6,173,107 describes a method and apparatus for installing or advancing a lightweight and flexible transmission line along a tubular pathway comprising insertion of the free end of such a line into a previously installed pathway, and propelling the line along the pathway by fluid drag of a gaseous medium passed through the pathway in the desired direction of advance. The present invention may also incorporate this method and potentially the apparatus as described below for the same purpose utilizing the central core of the support-separators for ABF or pulling with a pull tape.
It should be appreciated that to generate sufficient fluid drag to propel the transmission line, the gaseous medium has to be passed through the pathway with a flow velocity much higher than the desired rate of advance.
The terms “lightweight and flexible” with respect to the transmission line are to be understood as meaning “sufficiently lightweight and flexible” for the transmission line to be propelled by the fluid drag. The flow velocity of the gaseous medium may be steady or may be suitably varied, for example either between a first velocity producing no, or insufficient, fluid drag to propel the fiber or wire member, and a second velocity producing sufficient fluid drag to propel the fiber or wire member, or between a first and second velocity both producing sufficient fluid drag for propelling the fiber or wire member. Conveniently the variations in velocity take the form of repeated abrupt changes between the first and second velocity. The aforementioned variations in flow velocity may include periods during which the flow is reversed with respect to the desired direction of advance of the transmission line.
It is to be understood that more than one transmission line may be propelled along the same tubular pathway.
A transmission line may, for example, comprise a single optical fiber or wire, protected by at least a primary coating but preferably contained within an outer envelope. Alternatively, a fiber or wire member may comprise a plurality of optical fibers or wires contained within a common envelope. The envelope may loosely or tightly surround the fiber (wire), or fibers (wires).
The method may be used for insertion of an optical fiber or wire member into, or its withdrawal from, the pathway.
The gaseous medium is chosen to be compatible with the environment in which the invention is performed, and in ordinary environments will be a non-hazardous gas or gas mixture. With the proviso about compatibility with the environment, the gaseous medium is preferably air or nitrogen.
The tubular pathways and/or the fiber or wire members are conveniently but not necessarily of circular cross-section, and the fiber or wire member is always smaller than the pathway. In practice, when installing an optical fiber member, the pathway internal diameter will generally be greater, and frequently much greater than 1 mm, and the external diameter of the fiber member greater than 0.5 microns.
A preferred range of diameters for the pathway is 1 to 10 mm, conveniently between 3 and 7 mm, and a preferred range of diameters for the fiber members is 1 to 4 mm, although much larger diameters may be used provided the fiber member is sufficiently lightweight and flexible. The diameter of the fiber member or members is preferably chosen to be greater than one tenth, and conveniently to be about one half of the pathway diameter or greater (and appropriately less, of course, if more than one fiber member is to be propelled through the same pathway). For single mode fiber the fiber and cladding diameter range is normally from 7-250 microns and for multimode fiber the range is normally between 250 and 900 microns.
Insertion of a fiber (or wire) member by means of the fluid drag of a gas passing over the fiber member has several advantages over methods involving pulling an optical fiber (wire) cable with a pull cord.
Firstly, the extra step of providing a pull cord or flat pull tape with a Kellum-like grip is eliminated.
Secondly, using the fluid drag of a gaseous medium produces a distributed pulling force on the fiber (wire) member. This is particularly advantageous if the installation route contains one or more bends. If, as would be the case with a pulling cord, the pulling force were concentrated at the leading end of the fiber member, any deviation of the pathway from a straight line would greatly increase friction between the fiber member and the internal walls of the pathway, and only a few bends would be sufficient to cause locking of the fiber. The distributed pulling force produced by the fluid drag, on the other hand, enables bends to be negotiated fairly easily, and the number of bends in a given installation is no longer of much significance.
Thirdly, the fluid drag substantially reduces overall pulling stress on the fiber (or wire) member and so permits the fiber (or wire) member to be of relatively simple and cheap construction.
Furthermore, because the fiber member is not subjected to any substantial pulling stress during installation, little allowance, if any, needs to be made for subsequent relaxation.
According to a further aspect of the invention described in U.S. Pat. No. 6,173,107, a method of installing a transmission line comprises installing a conduit having one or more ductlets providing tubular pathways. The ductlets described below, for the present invention, may be the central hollow regions of any shape associated with the support-separators described.
The communications route may be initially designed and upgraded according to a customer's needs or desires. For example, after installation of the communications cable with support-separator, wire members containing one or more lightweight and flexible wires initially may be propelled through a pathway using fluid drag. Thereafter, the route may be upgraded by installing further wire members and/or inserting, by the aforesaid method using fluid drag, one or more fiber members into the associated ductlets as required. It would also be possible to remove fiber from existing ducts and reinstall newer fiber or new conductors as needed. In some cases, it may be possible to remove the duct itself and re-install (or not depending on the need).
Installing optical fiber and/or wire transmission lines by this method has several advantages over conventional techniques.
First, since the conduit is installed without containing any optical fibers, conventional rope pulling and similar techniques may be freely employed for installing the conduit.
Second, the capacity can readily be adapted to requirements. Thus, while initially only one or two fiber or wire members may be sufficient to carry the traffic, multiple cables may contain a much larger number of ductlets than are required at the time of installation, and further fiber or other members may be inserted later on as and when needed. The support-separator of the present invention is cheap compared to the cost of the fibers, and spare ductlets to accommodate further fibers and/or wires as and when extra capacity is required can thus be readily incorporated without adding more than a small fraction to overall costs.
The method of the U.S. Pat. No. 6,173,107 invention also permits the installation of improved later generations of transmission lines. It is possible, for example, to install at first one or more fiber members incorporating multimode fibers, and at a later date add, or replace the installed multimode fiber members with fiber members incorporating monomode fibers. Installed fiber members may conveniently be withdrawn from the ductlet, and replacement fiber members be inserted by using the aforesaid method of propelling by fluid drag of a gaseous medium.
Alternatively, the support-separators may comprise a plurality of individual tubes enveloped by a common outer sheath.
It will be appreciated that the present invention largely avoids the risk, inherent in handling optical fiber cables with a large number of fibers, of accidentally damaging before or during installation in a single event a large number of expensive optical fibers.
The present invention also enables the installation of continuous optical fibers over several installation lengths without joints.
Furthermore, individual fiber members routed through the conduit can be routed, without requiring fiber joints, into different branches of the conduits at various junction points.
Finally, a unique construction of the blown fiber duct or ductlets is described in WO patent application 01/34366 entitled: “Flexible plastic Tubing Construction Having a Sight Glass Window.”
Accordingly, the tubing construction of the invention herein involved is particularly adapted for use in ABF applications and other cable or wire installations wherein the ability to view the cables or wires within the tubing is desired for installation, servicing, or administration. It is possible that the present invention could incorporate the principals of the 01/34366 invention as well.
In another illustrative embodiment of the 01/34366 invention, the tubing (or in the case of the present invention—the lining of the inner central hollow core extending along the length of the support-separator) includes a third sidewall segment formed integrally with the first and second segments as having inner surface, which defines a portion of tubing innermost surface. Such inner surface may be profiled as defining a series of radially-disposed longitudinal splines, ribs, or other projections. With respect to ABF installation, such projections have been observed to reduce surface area contact between the cable and tubing sidewall, which results in corresponding decreased friction as the cable is blown through the tubing. Such projections also develop a lower velocity boundary layer in the gas flow near the surface which has the tendency to direct the fiber into the higher velocity flow towards the center of the tubing. The end result is less drag on the tubing which facilitates long runs and direction changes such as around bends.
Advantages of the 01/34366 invention include a flexible plastic tubing construction which is provided as having a sight-glass capability without affecting the gross fire resistance, electrical conductivity, or other specified chemical without affecting the gross fire resistance, electrical conductivity, or other specified chemical or physical properties of the tubing. Additional advantages include a tubing construction which is economical to manufacture in long, continuous lengths, and which further is particularly adapted for use in ABF installations. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.
As described above, an additional purpose of the present invention is to form and allow the central hollow region of the support separator spacers of the communications cables to act as a duct for ABF in the event this is desirable for installation purposes. The materials used to construct the support separators can be solid, semi-solid, foamed, foamed with a solid skin, or hollow. The lining of the central hollow region can be composed of polybutylene terephthalate (PBT) or other known materials capable of providing a sufficient combination of lubricity and friction to ensure proper accommodation of blown fiber “post” installation. There may be a separate inner lining within the central ring portion and it is always possible that the inner lining can be used such as shown in FIG. 1B.
Many precautions are taken to resist the spread of flame and the generation of and spread of smoke throughout a building in case of an outbreak of fire. Clearly, cables must be designed to protect against loss of life and also minimize the costs of a fire due to the destruction of electrical and other equipment. Therefore, wires and cables for building installations are required to comply with the various flammability requirements of the National Electrical Code (NEC) in the U.S. as well as International Electrotechnical Commission (EIC) and/or the Canadian Electrical Code (CEC).
Cables intended for installation in the air handling spaces (i.e. plenums, ducts, etc.) of buildings are specifically required by NEC/CEC/IEC to pass the flame test specified by Underwriters Laboratories Inc. (UL), UL-910, or its Canadian Standards Association (CSA) equivalent, the FF6. The UL-910 and the FT6 represent the top of the fire rating hierarchy established by the NEC and CEC respectively. Also important are the UL 1666 Riser test and the IEC 60332-3C and D flammability criteria. Cables possessing these ratings, generically known as “plenum” or “plenum rated” or “riser” or “riser rated”, may be substituted for cables having a lower rating (i.e. CMR, CM, CMX, FT4, FTI or their equivalents), while lower rated cables may not be used where plenum or riser rated cables are required. Future ratings include the CMP-50 standard which is considered to the European requirement of the future.
Cables conforming to NEC/CEC/IEC requirements are characterized as possessing superior resistance to ignitability, greater resistance to contribute to flame spread and generate lower levels of smoke during fires than cables having lower fire ratings. Often these properties can be anticipated by the use of measuring a Limiting Oxygen Index (LOI) for specific materials used to construct the cable. Conventional designs of data grade telecommunication cable for installations in plenum chambers have a low smoke generating jacket material, e.g. of a specially filled PVC formulation or a fluoropolymer material, surrounding a core of twisted conductor pairs, each conductor individually insulated with a fluorinated insulation layer. Cable produced as described above satisfies recognized plenum test requirements such as the “peak smoke” and “average smoke” requirements of the Underwriters Laboratories, Inc., UL910 Steiner tunnel test and/or Canadian Standards Association CSA-FT6 (Plenum Flame Test) while also achieving desired electrical performance in accordance with EIA/TIA-568A for high frequency signal transmission.
While the above described conventional cable, including the Belden 1711A cable design, due in part to their use of fluorinated polymers, meets all of the above design criteria, the use of fluorinated polymers is extremely expensive and may account for up to 60% of the cost of a cable designed for plenum usage. A solid core of these communications cables contributes a large volume of fuel to a potential cable fire. Forming the core of a fire resistant material, such as with FEP (fluorinated ethylene-propylene), is very costly due to the volume of material used in the core, but it should help reduce flame spread over the 20 minute test period. Reducing the mass of material by redesigning the core and separators within the core is another method of reducing fuel and thereby reducing smoke generation and flame spread. For the commercial market in Europe, low smoke fire retardant polyolefin materials have been developed that will pass the EN (European Norm) 502666-Z-X Class B relative to flame spread, total heat release, related heat release, and fire growth rate. Prior to this inventive development, standard cable constructions requiring the use of the aforementioned expensive fluorinated polymers, such as FEP, would be needed to pass this rigorous test. Using low smoke fire retardant polyolefins or foamed low smoke semi-rigid PVC for specially designed separators used in cables that meet the more stringent electrical requirements for Categories 6 and 7 and also pass the new norm for flammability and smoke generation is also a further subject of the present invention.
Solid flame retardant/smoke suppressed polyolefins may also be used in connection with fluorinated polymers. Commercially available solid flame retardant/smoke suppressed polyolefin compounds all possess dielectric properties inferior to that of FEP and similar fluorinated polymers. In addition, they also exhibit inferior resistance to burning and generally produce more smoke than FEP under burning conditions. A combination of the two different polymer types can reduce costs while minimally sacrificing physio-chemical properties. An additional method that has been used to improve both electrical and flammability properties includes the irradiation of certain polymers that lend themselves to crosslinking. Certain polyolefins are currently in development that have proven capable of replacing fluoropolymers for passing these same stringent smoke and flammability tests for cable separators, also known as “cross-webs”. Dual insulation designs as previously mentioned are also useful in this application. Additional advantages with the polyolefins are reduction in cost and toxicity effects as measured during and after combustion.
Current separator designs must also meet the UL 910 flame and smoke criteria using both fluorinated and non-fluorinated jackets as well as fluorinated and non-fluorinated insulation materials for the conductors of these cable constructions. In Europe, the trend continues to be use of halogen free insulation for all components, which also must meet stringent flammability regulations. The test in Europe which the present inventive separators and subsequent cables should also pass is known as “B-1”.
A high performance communications data cable utilizing twisted pair technology must meet exacting specification with regard to data speed, electrical, as well as flammability and smoke characteristics. The electrical characteristics include specifically the ability to control impedance, near-end cross-talk (NEXT), ACR (attenuation cross-talk ratio) and shield transfer impedance. A method used for twisted pair data cables that has been tried to meet the electrical characteristics, such as controlled NEXT, is by utilizing individually shielded twisted pairs (ISTP). These shields insulate each pair from NEXT. Data cables have also used very complex lay techniques to cancel E and B (electric and magnetic fields) to control NEXT. In addition, previously manufactured data cables have been designed to meet ACR requirements by utilizing very low dielectric constant insulation materials. Use of the above techniques to control electrical characteristics have inherent problems that have lead to various cable methods and designs to overcome these problems.
Recently, the development of “high-end” electrical properties for Category 6 and 7 cables has increased the need to determine and include power sum NEXT (near end crosstalk) and power sum ELFEXT (equal level far end crosstalk) considerations along with attenuation, impedance, and ACR values. These developments have necessitated the development of more highly evolved separators that can provide offsetting of the electrical conductor pairs so that the lessor performing electrical pairs can be further separated from other pairs within the overall cable construction.
Recent and proposed cable standards are increasing cable maximum frequencies from 100-200 MHz to 250-700 MHz. In the case of the present invention, the intention is to meet design criteria so that the conductors are capable of carrying signals at or above 10 GHz. The maximum upper frequency of a cable is that frequency at which the ACR (attenuation/cross-talk ratio) is essentially equal to 1. Since attenuation increases with frequency and cross-talk decreases with frequency, the cable designer must be innovative in designing a cable with sufficiently high cross-talk. This is especially true since many conventional design concepts, fillers, and spacers may not provide sufficient cross-talk at the higher frequencies.
Individual shielding is costly and complex to process. Individual shielding is highly susceptible to geometric instability during processing and use. In addition, the ground plane of individual shields, 360° in ISTP's—individually shielded twisted pairs—is also an expensive process. Lay techniques and the associated multi-shaped anvils of the present invention to achieve such lay geometries are also complex, costly and susceptible to instability during processing and use. Another problem with many data cables is their susceptibility to deformation during manufacture and use. Deformation of the cable geometry, such as the shield, also potentially severely reduces the electrical and optical consistency. The “cross-web” designs currently in use provide primarily an unshielded pair, but it increase EMI/RFI shielding effectiveness, the present invention includes the use of “shielded cross-webs”.
Optical fiber cables exhibits a separate set of needs that include weight reduction (of the overall cable), optical functionality without change in optical properties and mechanical integrity to prevent damage to glass fibers. For multi-media cable, i.e. cable that contains both metal conductors and optical fibers, the set of criteria is often incompatible. The use of the present invention, however, renders these often divergent set of criteria compatible. Specifically, optical fibers must have sufficient volume in which the buffering and jacketing plenum materials (FEP and the like) covering the inner glass fibers can expand and contract over a broad temperature range without restriction, for example −40 C. to 80 C. experienced during shipping. It has been shown by that cyclical compression and expansion directly contacting the buffered glass fiber causes excess attenuation light loss (as measured in dB) in the glass fiber. The design of the present invention allows for designation and placement of optical fibers in clearance channels provided by the support-separator. It would also be possible to place both glass fiber and metal conductors in the same designated clearance channel if such a design is required. In either case the forced spacing and separation from the cable jacket (or absence of a cable jacket) would eliminate the undesirable set of cyclical forces that cause excess attenuation light loss. In addition, fragile optical fibers are susceptible to mechanical damage without crush resistant members (in addition to conventional jacketing). The present invention also addresses this problem and allows for “air” blown fiber ducts for installation of fiber optics at a later time in existing installations. Here “air” refers to any gas that can be used to convey fiber down the duct (or “tube”—an empty or hollow section of the separator).
The need to continue improving cable and cable separator designs by reducing costs and improving mechanical and electrical properties as well as flammability continues to exist.